1. Field of the Invention
The present invention relates to lighting apparatus and display apparatus using the same.
2. Description of Related Art
In display, optical communication and many other fields, there is a demand for alignment of relatively diverging light beams in a given direction. To meet this demand, lighting apparatus are generally provided with an optical sheet for controlling the directivity of light in a light exit port of a light source housing. The optical sheet is optically transparent and aligns incident light in a given direction. A typical example of such an optically transparent optical sheet for controlling the directivity of light is a prism sheet as disclosed in Japanese Unexamined Patent Application Publication No. 2004-281270, for example.
A normal prism sheet is formed of multiple triangular or half-barrel shaped prisms which control the direction of light beams by prism effects or lens effects. However, whatever shape the prisms of the prism sheets take, there is a limit to the control of the directivity of light as long as light beams enter the prism sheet from all angles. For example, when a lighting apparatus is used as a backlight of a liquid crystal display, a light focus angle is about ±30 degrees at smallest with respect to the normal to a liquid crystal surface, and it is difficult to focus light within a desired angle range. It is also difficult to increase the front luminance of a liquid crystal surface to double or higher.
A lighting apparatus using another example of an optical sheet is disclosed in Japanese Unexamined Patent Application Publication No. H02-214287, for example. This lighting apparatus uses a lenticular lens sheet that has a reflector on its backside. The lenticular lens sheet is attached to a housing (light box) that contains a light source, and the inner surface of the housing is highly reflective. The reflector on the backside of the lenticular lens sheet has openings (slots) arrayed in stripes, through which light from the light source exits outside. The invention disclosed in Japanese Unexamined Patent Application Publication No. H02-214287 is applicable to a micro lens sheet, in which case the openings are arranged in dots.
Furthermore, because such a prism sheet is normally formed by molding, changing the optical characteristics of the sheet requires changing the shape of a mold. A mold is generally expensive, and changing its shape leads to an increase in manufacturing costs of the prism sheet. In addition, manufacturing a prism sheet by the molding takes time to reduce the manufacturing efficiently. It is therefore difficult to design the sheet that can control the direction of light as desired.